The administration of pharmaceuticals for treating respiratory diseases, such as asthma, as well as agents for the prophylactic treatment and treatment of mucous membranes of the tracheobronchial tract is preferred. The administration of corticoids is possible here.
The variable flow rate limitation in lung diagnosis apparatuses is a further preferred field of application. This is possible for all measurement methods using, e.g., aerosol particles for the diagnosis.
DE-A-199 12 461 discloses a device for limiting the flow at low differential pressures, particularly for limiting the inhalation flow volume during the inhalation of therapeutic aerosols. The device consists of a housing including an inhalation opening, an exhalation opening and a flow channel arranged therebetween, said flow channel having a flat, oblong cross-section with flexible large-surface walls. Depending on the differential pressure between the exhalation opening and the inhalation opening and the flexibility of the wall material, the cross-section of the flow channel can be reduced in size to suit a predetermined maximum inhalation flow volume.
The administration of pharmaceuticals in the form of an aerosol to the lungs by inhalation is essentially influenced by four factors: (i) the particle size and particle properties of the aerosol; (ii) the breathing volume of the patient; (iii) the patient's breathing flow; and (iv) the patient's morphometry and respiratory system. Whereas aerosols in suitable particle sizes have been produced by conventional systems, the parameters “breathing volume” and “breathing flow” (rate of breathing) are taken into account either insufficiently or not at all. This leads to an uncontrolled inhalation of the aerosol, which in turn leads to the fact that an insufficient amount of aerosol particles reaches the lungs or does not reach the areas to be treated (e.g., alveolar area) within the lungs.
EP-A-0 965 355 discloses a device for controlled inhalational administration of controlled-dosage drugs into the lungs. Said controlled inhalator comprises a closed recipient adapted to be charged with a predeterminable aerosol volume and from which the aerosol may be withdrawn via a control means for controlling the inhalation flow. Said control means of this known inhalator is either an adjustable valve or a critical nozzle. The breathing flow can be limited by using an adjustable valve or a critical nozzle.
EP-B-0 050 654 discloses an inhalation apparatus for administering pulmonary medication. Said inhalation apparatus comprises an inflatable envelope from which aerosol can be inhaled through a mouthpiece. This aerosol is introduced via a nebuliser into the inflatable envelope from a cartridge prior to inhalation. The mouthpiece has a restriction to limit the amount of air flowing through the mouthpiece during inhalation. This restriction limits the breathing flow during inhalation.
The two mentioned inhalation devices are characterized in that there is a flow rate limitation, i.e., during the inspiratory phase the breathing flow increases only slowly and the increase in breathing flow decreases constantly, leading to a constant flattening of the curve in the graph of the breathing flow vs. time. This flow rate limitation leads to the fact that, depending on the patient's inspiratory capacity, the breathing flow increases differently up to a maximum flow value. Thus, the flow is nearly kept at a constant level. This means that in the known inhalators, the intended flow rate limitation may lead to a more constant aerosol deposition in the lungs.
EP-A-1 036 569 discloses a method of and a device for providing a constant medicament dose for an inhalational administration at a low inhalation flow rate. This device consists of a closed container reducible in terms of volume, a mouthpiece connected to the container, on which a powder-aerosol generator can be connected for availability of the aerosol, a housing reducible in terms of volume, which surrounds the container on all sides and from which the mouthpiece is led out in sealed form, and means for controlling the inlet and outlet of air into or out from the zone between the container and the housing. The housing is adapted to be changed from a volume compression condition into an envisaged expanded availability condition for creating the envisaged aerosol volume in the container.
Furthermore, DE-A-100 29 119 discloses a device for the flow limitation at low differential pressures, in particular for the limitation of the inhalation volume flow during the inhalation of therapeutic aerosols. This device consists of a housing with at least an inlet opening, at least an outlet opening and a flow channel with at least a flexible wall arranged therebetween, whose cross-section is reducible to a predetermined size for a predetermined maximum inhalation volume flow depending on the negative pressure prevailing between the inhalation and exhalation openings and the flexibility of the wall material.
EP-A-1 163 921 discloses an inhalation device with a self-expanding container for a predetermined aerosol volume, means for introducing aerosol from an aerosol dispenser into the container and control means for controlling the inhalation flow. The control means keeps the inhalation flow at an essentially constant level during the entire aerosol inhalation period, wherein the control means comprises four flow channels which are radially arranged between a central inlet opening and outlet openings which are radially spaced apart from the inlet opening. The four radial flow channels are formed by four radially arranged, rectangular ribs extending from an essentially rigid wall to an essentially flexible wall, wherein one rib is longer than the others.
It is important regarding the intended administering of pharmaceuticals in the field of aerosol therapy that a certain inhalation volume flow is not exceeded. At the same time the patient's work of breathing at the inhalation device should be as little as possible. This means that during inspiration the patient should not have to create a great negative pressure so that the inhalation can also be performed by patients with bad lung function. In order to ensure the mobility of the patients, especially inhalators for administering emergency pharmaceuticals such as, e.g., fast acting beta-2-sympathomimetica, have to be administered with small handy inhalation devices. Prior art systems, however, could not integrate a breathing flow control in hand-held units due to the big dimensions of the flow rate limitation valves. Conventional dosed aerosol inhalation systems, be it for fluid or dry powder aerosols, exhibit a compact design, mostly operable with one hand. Such inhalation systems have no device to prevent the negative effect of a too high air flow on a good active ingredient deposition. An intended volume flow limitation during inhalation of therapeutic aerosols cannot be achieved in hand-held devices.